Analog self-interference cancellation systems for cmts

ABSTRACT

A system for wired analog self-interference cancellation includes a coarse delayer that delays a sampled RF transmit signal by a first delay amount; a frequency downconverter that downconverts the sampled RF transmit signal to IF; a first canceller tap group comprising a first per-tap-group delayer, a first sampling coupler, a first per-tap delayer, and first and second analog vector modulators that generates an IF self-interference cancellation signal; a frequency upconverter that upconverts the IF self-interference cancellation signal to RF; and a receive coupler that combines the RF self-interference cancellation signal with the RF receive signal, reducing self-interference.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 62/539,716, filed on 1 Aug. 2017, and of U.S. ProvisionalApplication Ser. No. 62/634,340, filed on 23 Feb. 2018, which isincorporated in its entirety by this reference.

TECHNICAL FIELD

This invention relates generally to the electronic communications field,and more specifically to new and useful analog self-interferencecancellation systems for CMTS.

BACKGROUND

Traditional cable modems operate using frequency-division duplexedcommunications; that is, communication from the cable modems to theircorresponding cable modem termination system (CMTS) (i.e., uplinkcommunication) occurs in a different frequency band than communicationsfrom the CMTS to the cable modem (i.e., downlink communication). Recentwork in the electronic communications field has led to advancements indeveloping full-duplex communications systems; these systems, ifimplemented successfully, could allow for more efficient allocation ofcommunication in a given bandwidth spectrum. One major roadblock tosuccessful implementation of full-duplex communications is the problemof self-interference. While progress has been made in this area, manysolutions intended to address self-interference are less than ideal forthe particular needs of cable modem communication. Thus, there is a needin the electronic communications field to create new and useful analogself-interference cancellation systems for CMTS. This invention providessuch new and useful systems.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a diagram view of a CMTS distribution system;

FIG. 1B is a spectral diagram view of a frequency division of a CMTSdistribution system;

FIG. 2A is a spectral diagram view of a frequency division of a CMTSdistribution system;

FIG. 2B is a spectral diagram view of a frequency division of a CMTSdistribution system;

FIG. 3A is a spectral diagram view of a frequency division of a CMTSdistribution system;

FIG. 3B is a spectral diagram view of a frequency division of a CMTSdistribution system;

FIG. 4 is a schematic view of a system of an invention embodiment;

FIG. 5 is a schematic view of an analog self-interference canceller of asystem of an invention embodiment;

FIG. 6 is a schematic view of an analog self-interference canceller of asystem of an invention embodiment;

FIG. 7 is a schematic view of an analog self-interference canceller of asystem of an invention embodiment;

FIG. 8A is a schematic view of an analog self-interference canceller ofa system of an invention embodiment;

FIG. 8B is a schematic view of an analog self-interference canceller ofa system of an invention embodiment;

FIG. 9 is a diagram view of reflections of a CMTS distribution system;

FIG. 10 is a schematic view of an analog self-interference canceller ofa system of an invention embodiment;

FIG. 11A is a schematic view of a delayer of a system of an inventionembodiment;

FIG. 11B is a schematic view of a delayer of a system of an inventionembodiment; and

FIG. 12 is a schematic view of a delayer of a system of an inventionembodiment.

DESCRIPTION OF THE INVENTION EMBODIMENTS

The following description of the invention embodiments of the inventionis not intended to limit the invention to these invention embodiments,but rather to enable any person skilled in the art to make and use thisinvention.

1. Self-Interference Cancellation for CMTS

As shown in FIG. 1A, traditional cable modem termination systems (CMTSs)communicate with several cable modems connected to the same coaxialcable system, splitting bandwidth between the modems; this bandwidthsplit is as shown in FIG. 1B. M1 UL refers to upload bandwidth for thefirst cable modem (M1) (i.e., transmissions from M1 to CMTS), M1 DLrefers to download bandwidth for the first cable modem (M1) (i.e.,transmissions from CMTS to M1), etc..

The systems of the present application are directed to enablingfull-duplex communications between CMTSs and cable modems. Suchfull-duplex communications could result in greater available bandwidthfor communications. For example, full-duplex communications could beimplemented at the CMTS but not at cable modems, allowing for there-allocation of bandwidth across modems. For example, if bandwidthallocation is kept the same per-mode, an additional modem couldcommunicate in the same spectrum, as shown in FIG. 2A. Alternatively,bandwidth may be increased per-modem, as shown in FIG. 2B. In thisscenario, while the CMTS can receive and transmit at the samefrequencies (e.g., M2 DL and M1 UL), the modem cannot (so M1 DL and ULmust be frequency separated, for instance).

Full-duplex communications may alternatively be implemented at both CMTSand Cable modems. Such an implementation may be purely full duplex, asshown in FIG. 3A, or take a hybrid approach, as shown in FIG. 3B. Inthis scenario, while both of the CMTS and modems can receive andtransmit at the same frequencies (e.g., M2 DL and M1 UL).

Full-duplex communications may additionally or alternatively beimplemented in any manner (e.g., at modems and not at a CMTS).

While full-duplex communications systems have substantial value to thecommunications field, such systems have been known to face challengesdue to self-interference; because reception and transmission occur atthe same time on the same channel, the received signal at a full-duplextransceiver can include undesired signal components from the signalbeing transmitted from that transceiver (e.g., resulting fromreflections at cable couplings or due to transmission line defects). Asa result, full-duplex communications systems often include analog and/ordigital self-interference cancellation circuits to reduceself-interference.

Full-duplex transceivers preferably sample transmission output asbaseband digital signals, intermediate frequency (IF) analog signals, oras radio-frequency (RF) analog signals, but full-duplex transceivers canadditionally or alternatively sample transmission output in any suitablemanner (e.g., as IF digital signals). This sampled transmission outputcan be used by full-duplex transceivers to remove interference fromreceived communications data (e.g., as RF/IF analog signals or basebanddigital signals). In many full-duplex transceivers, an analogself-interference cancellation system is paired with a digitalself-interference cancellation system. The analog self-interferencecancellation system removes a first portion of self-interference bysumming delayed, phase shifted and scaled versions of the RF transmitsignal to create an RF self-interference cancellation signal, which isthen subtracted from the RF receive signal. Alternatively, the analogcancellation system can perform similar tasks at an intermediatefrequency. After the RF (and/or IF) receive signal has the RF/IFself-interference cancellation signal subtracted, it passes through ananalog-to-digital converter of the receiver (and becomes a digitalreceive signal). After this stage, a digital self-interferencecancellation signal (created by transforming a digital transmit signal)is then subtracted from the digital receive signal.

The systems of the present disclosure are preferably designed to enablefull-duplex communications for cable modem/CMTS communications. Comparedto typical wireless applications, the frequency range of operationgenerally extends substantially lower in the radio frequency spectrum(e.g., 5 MHz to 1000 MHz). Further, because wired communications is lesslossy (and self-interference occurs largely from echoes), longertime-delayed reflections may contribute to self-interference in cablecommunications than in wireless communications. The systems of thepresent disclosure are preferably specially adapted to these conditions,but may additionally or alternatively be used and/or adapted for anyother applicable systems, including active sensing systems (e.g.,RADAR), wired communications systems, wireless communications systems,channel emulators, reflectometers, PIM analyzers and/or any othersuitable measurement equipment system, including communication systemswhere transmit and receive bands are close in frequency, but notoverlapping, or even TDD (time division duplex) systems.

2. Self-Interference Cancellation System for CMTS

As shown in FIG. 4, a system 100 for self-interference cancellation forCMTS includes a transmit coupler 110, an analog self-interferencecanceller 120, and a receive coupler 111. The system 100 mayadditionally or alternatively include a digital self-interferencecanceller 130 and/or a controller 140.

The system 100 functions to increase the performance of full-duplextransceivers (or other applicable systems) by performingself-interference cancellation.

The system 100 may perform self-interference cancellation by performinganalog and/or digital self-interference cancellation based on any numberof sampled analog and/or digital transmit signals. For example, thedigital self-interference canceller 130 may sample a digital transmitsignal, as shown in FIG. 4, but the digital self-interference canceller130 may additionally or alternatively sample an analog transmit signal(e.g., through an ADC coupled to the analog transmit signal).

The system 100 preferably performs analog and digital self-interferencecancellation simultaneously and in parallel, but may additionally oralternatively perform analog and/or digital self-interferencecancellation at any suitable times and in any order.

The system 100 is preferably implemented using both digital and analogcircuitry. Digital circuitry is preferably implemented using ageneral-purpose processor, a digital signal processor, an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA) and/or any suitable processor(s) or circuit(s). Analog circuitryis preferably implemented using analog integrated circuits (ICs) but mayadditionally or alternatively be implemented using discrete components(e.g., capacitors, resistors, transistors), wires, transmission lines,transformers, couplers, hybrids, waveguides, digital components,mixed-signal components, or any other suitable components. Both digitaland analog circuitry may additionally or alternatively be implementedusing optical circuitry (e.g., photonic integrated circuits). The system100 preferably includes memory to store configuration data, but mayadditionally or alternatively be configured using externally storedconfiguration data or in any suitable manner.

The system 100 preferably is coupled to a receiver. The receiverfunctions to receive analog receive signals transmitted over acommunications link (e.g., a coaxial cable, a wireless channel). Thereceiver preferably converts analog receive signals into digital receivesignals for processing by a communications system, but may additionallyor alternatively not convert analog receive signals (passing themthrough directly without conversion).

The receiver is preferably a radio-frequency (RF) receiver, but mayadditionally or alternatively be any suitable receiver. The receiver ispreferably coupled to the communications link by a duplexer-coupledcoaxial cable, but may additionally or alternatively be coupled to thecommunications link in any suitable manner.

The receiver preferably includes an analog-to-digital converter (ADC)and a frequency downconverter. The receiver may additionally include alow-noise amplifier. The receiver may additionally or alternativelyinclude amplifiers, filters, signal processors and/or any other suitablecomponents. In one variation of a preferred embodiment, the receiverincludes only analog processing circuitry (e.g., amplifiers, filters,attenuators, delays). The receiver may function to scale, shift, and/orotherwise modify the receive signal. The downconverter functions todownconvert the analog receive signal from RF (or any other suitablefrequency) to a baseband or IF analog receive signal, and theanalog-to-digital converter (ADC) functions to convert the baseband orIF analog receive signal to a digital receive signal.

Likewise, the system 100 is preferably also coupled to a transmitter.The transmitter functions to transmit signals of the communicationssystem over a communications link to a second communications system. Thetransmitter preferably converts digital transmit signals into analogtransmit signals.

The transmitter is preferably a radio-frequency (RF) transmitter, butmay additionally or alternatively be any suitable transmitter.

The transmitter is preferably coupled to the communications link by adirectionally-coupled coaxial cable, but may additionally oralternatively be coupled to the communications link in any suitablemanner.

The transmitter preferably includes a digital-to-analog converter (DAC)and a frequency upconverter. The transmitter may additionally include apower amplifier. The transmitter may additionally or alternativelyinclude amplifiers, filters, signal processors and/or any other suitablecomponents. The transmitter may function to scale, phase shift, delay,and/or otherwise modify the transmit signal. The digital-to-analogconverter (DAC) functions to convert the digital transmit signal to abaseband or IF analog transmit signal, and the upconverter functions toupconvert the baseband or IF analog transmit signal from baseband or IFto RF (or any other intended transmission frequency).

The transmit coupler 110 functions to provide a sample of the analogtransmit signal for the analog canceller 120 and/or the digitalcanceller 130. Transmit couplers may additionally be used to split powerbetween signal paths (e.g., splitting power between different analogcanceller 120 blocks).

The transmit coupler 110 is preferably a short section directionaltransmission line coupler, but may additionally or alternatively be anypower divider, power combiner, directional coupler, or other type ofsignal splitter. The transmit coupler 110 is preferably a passivecoupler, but may additionally or alternatively be an active coupler (forinstance, including power amplifiers). For example, the transmit coupler110 may comprise a coupled transmission line coupler, a branch-linecoupler, a Lange coupler, a Wilkinson power divider, a hybrid coupler, ahybrid ring coupler, a multiple output divider, a waveguide directionalcoupler, a waveguide power coupler, a hybrid transformer coupler, across-connected transformer coupler, a resistive or capacitive tee,and/or a resistive bridge hybrid coupler. The output ports of thetransmit coupler 110 are preferably phase-shifted by ninety degrees, butmay additionally or alternatively be in phase or phase shifted by anyamount (e.g., zero degrees, 180 degrees).

Transmit couplers 110 may be arranged in series and/or in parallel. Theconfiguration of multiple transmit couplers no in the system 100 isdiscussed in further detail in Section 3 (Self-Interference CancellationSystem Configurations).

The receive coupler 111 functions to combine one or more analogself-interference cancellation signals (from analog/digital cancellers)with the analog receive signal.

The receive coupler 111 is preferably a short section directionaltransmission line coupler, but can additionally or alternatively be anypower divider, power combiner, directional coupler, or other type ofsignal splitter. The receive coupler 111 is preferably a passivecoupler, but can additionally or alternatively be an active coupler (forinstance, including power amplifiers). For example, the receive coupler111 can comprise a coupled transmission line coupler, a branch-linecoupler, a Lange coupler, a Wilkinson power divider, a hybrid coupler, ahybrid ring coupler, a multiple output divider, a waveguide directionalcoupler, a waveguide power coupler, a hybrid transformer coupler, across-connected transformer coupler, a resistive tee, and/or a resistivebridge hybrid coupler. The output ports of the receive coupler 111 arepreferably phase-shifted by ninety degrees, but can additionally oralternatively be in phase or phase shifted by any amount (e.g., zerodegrees, 180 degrees).

The analog self-interference canceller 120 functions to produce ananalog self-interference cancellation signal from the analog transmitsignal that can be combined with the analog receive signal to reduceself-interference present in the analog receive signal. Prior toself-interference cancellation, the receive signal may contain both oreither of an intended receive signal and self-interference. Afterself-interference cancellation, the receive signal (which may now bereferred to as a “composite” receive signal, as it is the result of thecombination of the receive signal and the self-interference cancellationsignal) preferably still contains the intended receive signal (if oneexists), and any remaining self-interference may be referred to asresidual self-interference. The analog self-interference canceller 120is preferably designed to operate at a single intermediate frequency(IF) band, but may additionally or alternatively be designed to operateat multiple IF bands, at one or multiple radio frequency (RF) bands, orat any suitable frequency band.

The analog self-interference canceller 120 is preferably implemented asone or more analog circuits that transform an RF transmit signal into ananalog self-interference cancellation signal by combining a set offiltered, scaled, phase-shifted, and/or delayed versions of the RFtransmit signal, but may additionally or alternatively be implemented asany suitable circuit. For instance, the analog self-interferencecanceller 120 may perform a transformation involving only a singleversion or copy of the RF transmit signal. The transformed signal (theanalog self-interference cancellation signal) preferably represents atleast a part of the self-interference component received at thereceiver.

The analog self-interference canceller 120 is preferably adaptable tochanging self-interference parameters in addition to changes in theanalog transmit signal; for example, RF transceiver temperature, ambienttemperature, wiring configuration, humidity, and RF transmitter power.Adaptation of the analog self-interference canceller 120 is preferablyperformed by a tuning circuit, but may additionally or alternatively beperformed by a control circuit or other control mechanism included inthe canceller 120, the controller 140, or any other suitable controller.

In one implementation of an invention embodiment, the analogself-interference canceller includes sampling couplers 121, analogvector modulators 122, delayers 123, and combining couplers 124, asshown in FIG. 5. The analog self-interference canceller may additionallyor alternatively include frequency downconverters 125, frequencyupconverters 126, and/or amplifiers 127. In this implementation, theanalog self-interference canceller 120 splits the transmit signal intosignal paths using the sampling couplers 121 and transforms each ofthese signal paths (also referred to as ‘taps’) individually beforerecombining them at combining couplers 124. Note that taps may beorganized into tap groups, as shown in FIG. 5, or in any other manner.

Note that in some cases, the signal paths can be filtered such thatsignal paths can operate on different frequency sub-bands. The frequencysub-bands can overlap in frequency; there can additionally oralternatively be multiple filters corresponding to the same frequencysub-band. In such implementations the canceller 120 may include filters.

The analog self-interference canceller 120 preferably transforms eachtap by phase-shifting and/or scaling the signal components of each tapwith a vector modulator 122 in addition to delaying signal componentswith delayers 123. The components of the analog self-interferencecanceller 120 be coupled in any manner that enables analogself-interference cancellation for the system 100. The analogself-interference canceller 120 may include any components coupled inany manner.

Sampling couplers 121 function to split the transmit signal (or othersignal components) into multiple transmit signal paths. Samplingcouplers 121 preferably split an input signal into multiple signalshaving substantially the same waveform as the input signal; power may besplit among output signals in any manner. For example, as shown in FIG.6, sampling coupler 121 a and 121 b have two 3 dB ports, while samplingcoupler 121C has one −1.25 dB port and one '6 dB port. In this example,the signal component at vector modulator 122 a has a signal level of −6dB relative to the transmit signal, the signal component at 122 b has−7.25 dB, and the signal component at 122C has −12 dB.

The sampling coupler 121 is preferably a transmission line powerdivider, but may additionally or alternatively be any suitable powerdivider, splitter, or coupler. The sampling coupler 121 may additionallycontain any suitable electronics for pre-processing the transmit signal;for example, the sampling coupler 121 may contain an amplifier toincrease the power contained in one or more of the output transmitsignals.

Each analog canceller 120 block preferably includes a sampling coupler121; additionally or alternatively, analog canceller 120 blocks mayshare one or more sampling couplers 121.

The vector modulator 122 functions to phase shift and/or scale signalcomponents of the analog self-interference canceller 120. The vectormodulator 122 may perform one or more of phase shifting, phaseinversion, amplification, and attenuation. Phase shifting can allow thecanceller 120 to reflect the contribution of multiple signal componentswith offset phase, while signal scaling (e.g., attenuation,amplification, inversion) enables the canceller to appropriately matchself-interference cancellation signal components to predicted orobserved self-interference present in receive signals.

When scaling, the vector modulator 122 effectively multiplies thetransmit signal components by a scale factor. For example, anattenuation of 34% might be represented as a scale factor of 0.66; again of 20% might be represented as a scale factor of 1.20; and anattenuation of 10% and a phase inversion might be represented as a scalefactor of −0.90. Scale factors may be complex; for example, a scalefactor of ê (i*Pi/2) might be represented as a phase shift of ninetydegrees.

Each vector modulator 122 preferably includes an impedance matchingnetwork at its input and output that compensates for variations in thevector modulator 122 input and output impedance (and/or phase shiftamount) due to changes in signal component frequency or simplytransforms the impedance to and from a suitable impedance level for thecore of the phase shifter to a standardized impedance level (50 ohms).Alternatively, the vector modulator 122 may not include impedancematching networks. The impedance matching networks are preferablytunable (e.g., continuously or discretely variable) but may additionallyor alternatively be static (i.e., the impedance transformation achievedby using the network is not variable).

The vector modulator 122 may generate output signal components using anysuitable combination of circuit components. These components may bediscrete (e.g., capacitors, inductors) or integrated (e.g., a singleelement with a fixed capacitance, inductance, and resistance), or anyother suitable circuit components.

For example, a phase shifting stage of a vector modulator 122 maycomprise an LC network (e.g., an LC tank circuit), including aninductive element and a capacitive element, which is coupled toadditional phase shifting stages by a coupling capacitive element.Alternatively, such LC network stages may be magnetically coupledtogether by an inductive element (e.g., the inductive element of the LCtank, a separate coupling inductor, etc.). Alternatively oradditionally, phase shifting stages may include tunable phase-shiftelements (e.g., tunable capacitors, tunable inductors, etc.). Forexample, a phase shifting stage may include a varactor; by changing acontrol voltage of the varactor, the varactor's capacitance (and thusthe amount of phase shift experienced by a signal passing through thestage) may be varied. In a related example, each phase shifting stagecan be coupled to another phase shifting stage by a shunt varactor(e.g., the phase shifting stages are arranged in series, and each seriespair of phase shifting stages are coupled by shunt varactors).

Scaling stages of the vector modulator 122 may include attenuators,amplifiers, phase inverters, and/or any other suitable components forscaling transmit signal components. Attenuators may be resistiveattenuators (T pad, Pi pad, Bridged-T), capacitive dividers, amplifierswith less than unity gain, or any other suitable type of attenuator.Amplifiers may be transistor amplifiers, vacuum tube amplifiers,op-amps, or any other suitable type of amplifier. Phase inverters may beany phase inversion devices, including NPN/PNP phase inversion circuits,transformers and/or inverting amplifiers.

The vector modulators 122 preferably are capable of phase shift,attenuation, gain, and phase inversion, but may alternatively be capableonly of a subset of said capabilities. Each vector modulator 122preferably includes all four capabilities in a single device but mayadditionally or alternatively separate capabilities into differentsections (e.g., an amplifier with tunable gain but no inversioncapability, along with a separate phase shifting circuit). The vectormodulator 122 is preferably controlled by a tuning circuit or thecontroller 140, but may additionally or alternatively be controlled inany suitable manner.

The delayers 123 function to delay transmit signal components,preferably to match corresponding delays in received self-interference.The delay introduced by each delayer 123 (also referred to as a delayerdelay) is preferably fixed (i.e., the delayer 123 is a fixed delayer),but delayers 123 can additionally or alternatively introduce variabledelays. The delayer 123 is preferably implemented as an analog delaycircuit (e.g., a bucket-brigade device, a long transmission line,RC/LC/RLC networks, surface acoustic wave (SAW) delay lines, a filter oran optical delay line) but can additionally or alternatively beimplemented in any other suitable manner. If the delayer 123 is avariable delayer, the delay introduced is preferably set by a tuningcircuit, but can additionally or alternatively be set in any suitablemanner.

The delayers 123 may cover the full band or only partial (sub-) bands;e.g. if it reduces cost or improves performance the total bandwidth ofthe delay may be split up and suitable sub-band SAW devices may be used.

Additionally, in order to reduce the number of different delay devicesin the bill of material (BOM) or to reduce cost or increase performance,these different sub-bands may be converted into one preferred sub-bandvia frequency conversion (mixing) and afterwards separated again.

Each delayer 123 preferably includes an impedance matching network atits input and output that compensates for variations in the delayer 123input and output impedance (and/or delay amount) due to changes insignal component frequency or transforms the impedance to and from asuitable impedance level for the core of the delayer to a standardizedimpedance level (50 ohms). Alternatively, the delayer 123 cannot includeimpedance matching networks. The impedance matching networks arepreferably tunable (e.g., continuously or discretely variable) but canadditionally or alternatively be static (i.e., the impedancetransformation achieved by using the network is not variable).

Note that changes in phase shift can affect delays (and vice versa), sothe vector modulator 122 and delayer 123 are preferably tunedcooperatively (e.g., if a phase shifting value is changed, a delayervalue can also be changed to compensate for unintended delays introducedby the phase shift).

After transformation by a vector modulator 122 and/or a delayer 123,transmit signal components are transformed into self-interferencecancellation signal components, which can be combined to form aself-interference cancellation signal.

Combining couplers 124 function to combine the self-interferencecancellation signal components to generate an analog self-interferencecancellation signal; the analog self-interference cancellation signalcan then be combined with an analog receive signal to removeself-interference. The combining coupler 124 preferably combinesself-interference cancellation signal components (resulting frommultiple signal paths) and outputs the resulting analogself-interference cancellation signal. The combining coupler 124 ispreferably a transmission line coupler, but can additionally oralternatively be any suitable type of coupler (described in the samplingcoupler 121 sections). The combining coupler 124 can additionallycontain any suitable electronics for post-processing theself-interference cancellation signal before outputting it; for example,the combining coupler 124 can contain an amplifier to increase the powerof the self-interference cancellation signal. The combining coupler 124may combine signal components to form signals (e.g., self-interferencecancellation signal components can be combined to form aself-interference cancellation signal) but may additionally oralternatively combine signal components to form signal super-components,which can later be combined to form signals. Note that there is not anyinherent physical difference between signal components, signalsuper-components, and signals; different terms are used to identify howa signal or signal component is ultimately used. For example, a set offirst and second signal components may be combined to form a firstsuper-component, a set of third and fourth signal components may becombined to form a second super-component, and the first and secondsuper-components may be combined to form a signal (or asuper-super-component if later combination was to occur, etc.).

The canceller 120 may also contain one or more linearization circuits tocompensate for non-linearity generated in the self-interferencecanceller 120; as for example in amplifiers, switches, mixers, scalers,phase shifters and delayers.

As previously mentioned, the analog self-interference canceller 120 canperform self-interference cancellation at either or both of IF or RFbands. If the analog self-interference canceller 120 performscancellation at IF bands, the analog self-interference canceller 120preferably includes a downconverter 125 and an upconverter 126, as shownin FIGS. 7, 8A, and 8B. Note that as shown in FIG. 7, the entirecanceller 120 may be in the IF domain; while alternatively, as shown inFIGS. 8A and 8B, some aspects of the canceller 120 (e.g., the firstdelayer 123) may be in the RF domain. Note further that the analogself-interference canceller 120 may include separate frequencyconverters operating at different frequencies, as shown in FIG. 8B. Insuch an implementation, different signal paths may be used to processdifferent RF frequency bands simultaneously. The canceller 120 mayfeature any components operating at any frequency bands. Note thatdelays at RF frequency may be desirable for maintaining a high level ofaccuracy of the delayed signal, while IF or optical delays may providebenefits in accommodating more flexible frequency use and widerbandwidths with a smaller area. Delaying may be performed at anyfrequency in any scenario, however.

The downconverter 125 functions to downconvert the carrier frequency ofan RF transmit signal component to an intermediate frequency (or, insome cases, baseband (IF=0 Hz)) preparing it for transformation by theanalog canceller 120. The downconverter 125 is preferably substantiallysimilar to the downconverter of the receiver (although details such asLO frequency, linearity and filter configuration can differ between thetwo), but can additionally or alternatively be any suitable frequencydownconverter. Alternatively downconverters 125 may be used for anysignal downconversion.

The upconverter 126 functions to upconvert the carrier frequency of theIF self-interference cancellation signal (received from the analogcanceller 140) to a radio frequency, preparing it for combination withthe RF receive signal at the receiver. The upconverter 26 is preferablycommunicatively coupled to the receiver and the analog canceller 120,and preferably receives IF self-interference cancellation signals fromthe analog canceller 120, upconverts the signal to a radio frequency,and passes the resulting RF self-interference cancellation signal to thereceiver. Alternatively upconverters 126 may be used for any signalupconversion.

Amplifiers 127 may be transistor amplifiers, vacuum tube amplifiers,op-amps, or any other suitable type of amplifier.

The digital self-interference canceller 130 functions to produce adigital self-interference cancellation signal from a digital transmitsignal. The digital self-interference cancellation signal is preferablyconverted to an analog self-interference cancellation signal (by a DAC)and combined with the analog self-interference cancellation signals tofurther reduce self-interference present in the RF receive signal at thereceiver 110. Additionally or alternatively, the digitalself-interference cancellation signal can be combined with a digitalreceive signal.

The digital self-interference canceller 130 preferably samples the RFtransmit signal of the transmitter using an ADC (additionally oralternatively, the canceller 130 can sample the digital transmit signalor any other suitable transmit signal) and transforms the sampled andconverted RF transmit signal to a digital self-interference signal basedon a digital transform configuration. The digital transformconfiguration preferably includes settings that dictate how the digitalself-interference canceller 130 transforms the digital transmit signalto a digital self-interference signal (e.g. coefficients of ageneralized memory polynomial used to transform the transmit signal to aself-interference signal).

The digital self-interference canceller 130 can be implemented using ageneral-purpose processor, a digital signal processor, an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA) and/or any suitable processor(s) or circuit(s). The digitalself-interference canceller 130 preferably includes memory to storeconfiguration data, but can additionally or alternatively be configuredusing externally stored configuration data or in any suitable manner. Inone implementation, the digital self-interference canceller 130 issubstantially similar to the digital self-interference canceller of U.S.patent application Ser. No. 14/456,320, filed 11 Aug. 2014, which isincorporated in its entirety by this reference.

The digital self-interference canceller 130 can couple to transmit andreceive signals in a number of ways. For example, the digitalself-interference canceller 130 can use a converted RF transmit signalas input as well as provide a converted digital self-interferencecancellation signal as output. As another example, the digitalself-interference canceller 130 can use the digital transmit signal asinput as a well as provide a digital self-interference cancellationsignal as output (directly to the digital receive signal). The digitalself-interference canceller can additionally or alternatively couple totransmit signals in any combination of digital and analog receivesignals.

Note that while these examples reference the RF transmit signal and RFreceive signal, the digital self-interference canceller 130 canadditionally or alternatively couple to IF transmit signals and/or IFself-interference cancellation signals.

The controller 140 functions to control the analog self-interferencecanceller 120, and in particular components thereof (e.g., delayers 123,the vector modulators 122). The controller 140 can additionally oralternatively function to control any portion of the system 100 (e.g.,the digital self-interference canceller 130). For example, thecontroller 140 may control switches or other configuration parameters ofdelayers 123.

In one implementation of an invention embodiment, the controller 140analyzes reflections from a transmitted signal to characterizereflection delay times. In this implementation the controller 140 mayadditionally or alternatively automatically set one or more coarsedelays in response to reflection analysis.

3. Self-Interference Cancellation System Configurations

As previously discussed, one of the considerations required forself-interference cancellation in cable communications is the uniquenature of the cable channel. As shown in FIG. 9, a CMTS modem seessparse reflections due to the coupling of cable modems to the main CMTStransmission/reception coaxial cable. For example, the first reflection(at the coupler) may have a 0 μs delay and loss of 10 dB, secondreflection may have a 0.5 μs is delay (i.e., it arrives at the receiver0.5 μs is after being transmitted) and a loss of 16 dB, 1.0 μs and 22 dBfor the third reflection, 1.2 μs and 29 dB for the fourth reflection,and so on.

While it is possible to provide cancellation across the entire delaytime, it may be overly cost or complexity prohibitive to do so. Forexample, to cancel over a bandwidth of 500 MHz and a reflection time of2 μs would require 1,000 taps (assuming 2 ns delay resolution).

In contrast, if some data is known about the reflections, it may bepossible to perform the same level of cancellation with far fewer taps.For example, if it is known, as in the previous example, that there arefour primary reflections (at 0, 0.5, 1.0, and 1.2 μs), the system 100may include four tap groups, each with its own associated coarse delay,as shown in FIG. 10. In turn, each tap group may feature a per-tap-groupvariable delay of 0-200 ns, and finally, taps may have set per-tapdelays (e.g., of 3.5 ns). Note that delayers 123 may be in parallel(e.g., the per-tap-group delays) or in series (e.g., the per-tap delays)or in any combination. Note that a per-tap-group delay is any delay atthe beginning of a canceller tap group and is typically larger thanper-tap delays (of which there may be multiple for a tap group).

The set delays of the system 100 (e.g., the delays of the first coarsedelayer 123) may be set based on an analysis of signal reflections on aparticular line (or some other measurement) or may be chosen based onparameters of the communications channel. For example, it maybe knownthat drop distances between couplers corresponds to known delays, sodelayer 123 values may be chosen based on drop distances between cablemodem couplers on a CMTS line.

Note that delayers may be described in terms of range (specified as adifference; e.g., a 2 μs range is any delay where the minimum andmaximum delay values are separated by 2 μs, a 0-2 μs delay is a delaywhere the minimum delay is 0 μs and the maximum delay is 2 μs) and/ordelay step (for a discretely variable delay, the difference betweenincrementally modified delays; e.g., a 0-2 μs delay with loons stepsmight be tunable to delays of 0, 200 ns, 400 ns . . . 1800 ns, 2000 ns).

In one implementation of an invention embodiment, a coarse delayer 123may feature a chain of amplified delays (e.g., delay blocks alternatedwith amplifiers 127), as shown in FIG. 11A. In the example as shown inFIG. 11A, the delayer 123 has a first input (I1) and four outputs (O1, a200 ns delay; O2, a 400 ns delay; O3, a 600 ns delay; and O4, an 800 nsdelay). This implementation of the delayer 123 may be useful as adelayer 123 positioned before a plurality of delay chains (e.g., thetopmost delayer 123 as shown in FIG. 10).

As another example, the delayer 123 may feature a set of multipleinputs. In the example as shown in FIG. 11B, the delayer 123 has asingle output (O1) and four inputs (I1, a 200 ns delay; I2, a 400 nsdelay; I3, a 600 ns delay; and I4, an 800 ns delay). This implementationof the delayer 123 may be useful as a delayer 123 positioned after aplurality of delay chains. Delay outputs and inputs may be generallyreferred to as delay coupling points. In an optimized implementation,the delay coupling points could be incorporated within the delaystructure for reduced area and lower loss in the circuit. Similarly, thedelay coupling may also be integrated into the amplifier structure.

The delayer 123 may have any number of signal inputs and/or outputs andmay split and/or combine signal components in any manner.

In one implementation, a per-tap-group delayer 123 may feature a set ofbypassable delay blocks, as shown in FIG. 12 (in this case, enabled byswitches 128 that switch between a delay block and a bypass). In thisimplementation, the positions of switches 128 may be used to determinethe delay between input and output of the delayer 123. Similarly to theprevious delayer 123 example, delay blocks may have uniform values;alternatively, delay blocks may have any value. For example, aper-tap-group delayer 123 of this structure may feature delay blockvalues of 128 ns, 64 ns, 32 ns, 16 ns, 8 ns, and 4 ns (binary encoding);this delayer may be set to 64 different values from 0 ns to 252 ns.

Delayers 123 may additionally or alternatively be configured/coded inany way (e.g., thermometer coding, hybrid thermometer coding), mayfeature any number of delay blocks of any value, any number ofamplifiers 127, and/or any number of switches 128. For example, adelayer 123 may be binary encoded; that is, the delayer may have a basestep (e.g., 6 ns) and each value in the delayer is 2^(n)×6 ns; e.g., 6ns, 12 ns, 24 ns, 48 ns, etc. This may be particularly useful in a chainof bypassable delay blocks, where a delay can be formed from utilizationof a subset of the delay blocks.

The methods of the preferred embodiment and variations thereof can beembodied and/or implemented at least in part as a machine configured toreceive a computer-readable medium storing computer-readableinstructions. The instructions are preferably executed bycomputer-executable components preferably integrated with a system forself-interference cancellation. The computer-readable medium can bestored on any suitable computer-readable media such as RAMs, ROMs, flashmemory, EEPROMs, optical devices (CD or DVD), hard drives, floppydrives, or any suitable device. The computer-executable component ispreferably a general or application specific processor, but any suitablededicated hardware or hardware/firmware combination device canalternatively or additionally execute the instructions.

As a person skilled in the art will recognize from the previous detaileddescription and from the figures and claims, modifications and changescan be made to the preferred embodiments of the invention withoutdeparting from the scope of this invention defined in the followingclaims.

We claim:
 1. A system for wired analog self-interference cancellationcomprising: a transmit coupler, communicatively coupled to a radiofrequency (RF) transmit signal of a wired communication system, thatsamples the RF transmit signal to create a sampled RF transmit signalhaving an RF carrier frequency; an analog-self-interference cancellercomprising: a first coarse delayer that delays the sampled RF transmitsignal by a first delay amount, resulting in a delayed sampled RFtransmit signal; wherein the first coarse delayer delays the sampled RFtransmit signal prior to frequency downconversion; a frequencydownconverter, comprising a mixer, a local oscillator, and anintermediate frequency (IF) filter, wherein the frequency downconverterconverts, by heterodyning, the delayed sampled RF transmit signal to adelayed sampled IF transmit signal having an IF carrier frequency,wherein the IF carrier frequency is less than the RF carrier frequency;and a first canceller tap group comprising a first per-tap-groupdelayer, a first sampling coupler, a first per-tap delayer, first andsecond analog vector modulators, and a first combining coupler; whereinthe first per-tap-group delayer further delays the delayed sampled IFtransmit signal; wherein the first sampling coupler splits the delayedsampled IF transmit signal, after the first per-tap-group delayer, intofirst and second IF transmit signal components; wherein the first analogvector modulator generates a first IF self-interference cancellationsignal component from the first IF transmit signal component; whereinthe first per-tap delayer delays the second IF transmit signalcomponent, resulting in a delayed second IF transmit signal component;wherein the second analog vector modulator generates a second IFself-interference cancellation signal component from the delayed secondIF transmit signal component; wherein the first combining couplercombines the first and second IF self-interference cancellation signalcomponents to generate an IF self-interference cancellation signal; afrequency upconverter comprising a mixer, a local oscillator, and an RFfilter, wherein the frequency upconverter converts, by heterodyning, theIF self-interference cancellation signal to an RF self-interferencecancellation signal having the RF carrier frequency; and a receivecoupler, communicatively coupled to an RF receive signal of the wiredcommunication system, that combines the RF self-interferencecancellation signal with the RF receive signal, resulting in an RFcomposite receive signal; wherein the RF composite receive signalcontains less self-interference than the RF receive signal.
 2. Thesystem of claim 1, wherein the first coarse delayer comprises adiscretely variable surface-acoustic-wave (SAW) delayer having a rangeof at least 1.5 microseconds.
 3. The system of claim 2, wherein thefirst coarse delayer has delay steps of at least 150 nanoseconds.
 4. Thesystem of claim 2, wherein the first coarse delayer comprises a chain ofamplified delays in series, each amplified delay of the chain coupled toa coarse delayer coupling point; wherein delays of the first coarsedelayer are varied based on selection of first delayer coupling points.5. The system of claim 4, wherein the first per-tap-group delayercomprises a chain of bypassable delay blocks; wherein each of thebypassable delay blocks comprises an LC delay and an amplifier; whereinthe bypassable delay blocks are binary encoded.
 6. The system of claim5, wherein the first per-tap-group delayer has a base step of betweenone and ten nanoseconds.
 7. The system of claim 5, wherein the firstper-tap delayer has a fixed delay.
 8. The system of claim 5, furthercomprising an analog self-interference canceller controller that adaptsconfiguration parameters of the analog self-interference canceller basedon at least one of transmit signal data, receive signal data, andenvironmental data; wherein the configuration parameters include tunableparameters of the first and second analog vector modulators and bypasssettings of the first per-tap-group delayer.
 9. The system of claim 8,wherein the selection of first delayer coupling points is set based onmeasured drop distances between cable modem couplers coupled to thesystem.
 10. The system of claim 8, wherein the selection of firstdelayer coupling points is set automatically by the analogself-interference canceller controller based upon analysis of primaryreflections observed at the system.
 10. A system for wired analogself-interference cancellation comprising: a transmit coupler,communicatively coupled to a radio frequency (RF) transmit signal of awired communication system, that samples the RF transmit signal tocreate a sampled RF transmit signal having an RF carrier frequency; ananalog-self-interference canceller comprising: a first coarse delayerthat generates a first delayed sampled RF transmit signal by delayingthe sampled RF transmit signal by a first delay amount and generates asecond delayed sampled RF transmit signal by delaying the sampled RFtransmit signal by a second delay amount; wherein the second delayamount is greater than the first delay amount; wherein the first coarsedelayer generates delayed sampled RF transmit signals prior to frequencydownconversion; a frequency downconverter, comprising a mixer, a localoscillator, and an intermediate frequency (IF) filter, wherein thefrequency downconverter converts, by heterodyning, the first and seconddelayed sampled RF transmit signals to first and second delayed sampledIF transmit signals having an IF carrier frequency, wherein the IFcarrier frequency is less than the RF carrier frequency; a firstcanceller tap group comprising a first per-tap-group delayer, a firstsampling coupler, a first per-tap delayer, and first and second analogvector modulators; wherein the first per-tap-group delayer furtherdelays the first delayed sampled IF transmit signal; wherein the firstsampling coupler splits the first delayed sampled IF transmit signal,after the first per-tap-group delayer, into first and second IF transmitsignal components; wherein the first analog vector modulator generates afirst IF self-interference cancellation signal component from the firstIF transmit signal component; wherein the first per-tap delayer delaysthe second IF transmit signal component, resulting in a delayed secondIF transmit signal component; wherein the second analog vector modulatorgenerates a second IF self-interference cancellation signal componentfrom the delayed second IF transmit signal component; a second cancellertap group comprising a second per-tap-group delayer, a second samplingcoupler, a second per-tap delayer, and third and fourth analog vectormodulators; wherein the second per-tap-group delayer further delays thesecond delayed sampled IF transmit signal; wherein the second samplingcoupler splits the second delayed sampled IF transmit signal, after thesecond per-tap-group delayer, into third and fourth IF transmit signalcomponents; wherein the third analog vector modulator generates a thirdIF self-interference cancellation signal component from the third IFtransmit signal component; wherein the second per-tap delayer delays thefourth IF transmit signal component, resulting in a delayed fourth IFtransmit signal component; wherein the fourth analog vector modulatorgenerates a fourth IF self-interference cancellation signal componentfrom the delayed fourth IF transmit signal component; and a combiningcoupler that combines the first, second, third, and fourth IFself-interference cancellation signal components to generate an IFself-interference cancellation signal; a frequency upconvertercomprising a mixer, a local oscillator, and an RF filter, wherein thefrequency upconverter converts, by heterodyning, the IFself-interference cancellation signal to an RF self-interferencecancellation signal having the RF carrier frequency; and a receivecoupler, communicatively coupled to an RF receive signal of the wiredcommunication system, that combines the RF self-interferencecancellation signal with the RF receive signal, resulting in an RFcomposite receive signal; wherein the RF composite receive signalcontains less self-interference than the RF receive signal.
 12. Thesystem of claim 11, wherein the combining coupler combines the first andsecond IF self-interference cancellation signal components to form afirst IF self-interference cancellation signal super-component; whereinthe combining coupler combines the third and fourth IF self-interferencecancellation signal components to form a second IF self-interferencecancellation signal super-component; wherein the combining couplergenerates the IF self-interference cancellation signal by combining thefirst and second IF self-interference cancellation signalsuper-components.
 13. The system of claim 11, wherein the first coarsedelayer comprises a chain of delays in series, each delay of the chaincoupled to coarse delayer coupling points; wherein delays of the firstcoarse delayer are varied based on selection of the delayer couplingpoints.
 14. The system of claim 13, wherein the first coarse delayertakes the sampled RF transmit signal as input at a first coarse delayercoupling point, outputs the first delayed sampled RF transmit signal ata second delayer coupling point, and outputs the second delayed sampledRF transmit signal at a third delayer coupling point; wherein the thirddelayer coupling point is farther along the chain of delays than thesecond delayer coupling point.
 15. The system of claim 14, wherein thesecond and third delayer coupling points are amplified by amplifiers ofthe first coarse delayer.
 16. A system for wired analogself-interference cancellation comprising: a transmit coupler,communicatively coupled to a radio frequency (RF) transmit signal of awired communication system, that samples the RF transmit signal tocreate a sampled RF transmit signal having an RF carrier frequency; ananalog-self-interference canceller comprising: a frequencydownconverter, comprising a mixer, a local oscillator, and anintermediate frequency (IF) filter, wherein the frequency downconverterconverts, by heterodyning, the sampled RF transmit signal to a sampledIF transmit signal having an IF carrier frequency, wherein the IFcarrier frequency is less than the RF carrier frequency; a samplingcoupler that splits the sampled IF transmit signal into first and secondsampled IF transmit signals; a first canceller tap group comprising afirst per-tap-group delayer, a first sampling coupler, a first per-tapdelayer, first and second analog vector modulators, and a first couplingcombiner; wherein the first per-tap-group delayer delays the firstsampled IF transmit signal; wherein the first sampling coupler splitsthe first sampled IF transmit signal, after the first per-tap-groupdelayer, into first and second IF transmit signal components; whereinthe first analog vector modulator generates a first IF self-interferencecancellation signal component from the first IF transmit signalcomponent; wherein the first per-tap delayer delays the second IFtransmit signal component, resulting in a delayed second IF transmitsignal component; wherein the second analog vector modulator generates asecond IF self-interference cancellation signal component from thedelayed second IF transmit signal component; wherein the first combiningcoupler combines the first and second IF self-interference cancellationsignal components to generate a first IF self-interference cancellationsignal super-component; a second canceller tap group comprising a secondper-tap-group delayer, a second sampling coupler, a second per-tapdelayer, third and fourth analog vector modulators, and a secondcombining coupler; wherein the second per-tap-group delayer delays thesecond sampled IF transmit signal; wherein the second sampling couplersplits the second sampled IF transmit signal, after the secondper-tap-group delayer, into third and fourth IF transmit signalcomponents; wherein the third analog vector modulator generates a thirdIF self-interference cancellation signal component from the third IFtransmit signal component; wherein the second per-tap delayer delays thefourth IF transmit signal component, resulting in a delayed fourth IFtransmit signal component; wherein the fourth analog vector modulatorgenerates a fourth IF self-interference cancellation signal componentfrom the delayed fourth IF transmit signal component; wherein the secondcombining coupler combines the third and fourth IF self-interferencecancellation signal components to generate a second IF self-interferencecancellation signal super-component; a frequency upconverter comprisinga mixer, a local oscillator, and an RF filter, wherein the frequencyupconverter converts, by heterodyning, the first and second IFself-interference cancellation signal super-components to first andsecond RF self-interference cancellation signal super-components havingthe RF carrier frequency; and a first coarse delayer that delays thefirst RF self-interference cancellation signal super-component by afirst delay amount, delays the second RF self-interference cancellationsignal super-component by a second delay amount, and combines the firstand second RF self-interference cancellation signal super-components togenerate an RF self-interference cancellation signal; wherein the seconddelay amount is greater than the first delay amount; and a receivecoupler, communicatively coupled to an RF receive signal of the wiredcommunication system, that combines the RF self-interferencecancellation signal with the RF receive signal, resulting in an RFcomposite receive signal; wherein the RF composite receive signalcontains less self-interference than the RF receive signal.
 17. Thesystem of claim 16, wherein the first coarse delayer comprises a chainof delays in series, each delay of the chain coupled to coarse delayercoupling points; wherein delays of the first coarse delayer are variedbased on selection of the coarse delayer coupling points.
 18. The systemof claim 17, wherein the first coarse delayer takes the first RFself-interference cancellation signal super-component as input at afirst coarse delayer coupling point, takes the second RFself-interference cancellation signal super-component as input at asecond coarse delayer coupling point, and outputs the RFself-interference cancellation signal at a third delayer coupling point;wherein the first delayer coupling point is between the second and thirdcoupling points along the chain of delays.
 19. The system of claim 18,wherein the selection of the coarse delayer coupling points is set basedon measured drop distances between cable modem couplers coupled to thesystem.
 20. The system of claim 18, wherein the selection of coarsedelayer coupling points is set automatically by an analogself-interference canceller controller based upon analysis of primaryreflections observed at the system.